Systemic lidocaine decreases the Bispectral Index in the presence of midazolam, but not its absence.

STUDY OBJECTIVE

To evaluate the effects of intravenous (IV) lidocaine on the Bispectral Index (BIS) in the presence or absence of midazolam.

DESIGN

Prospective, randomized, double-blinded, placebo-controlled clinical study.

SETTING

Operating room of a university hospital.

PATIENTS

96 ASA physical status 1, 2, and 3 patients undergoing general anesthesia.

INTERVENTIONS

Patients were assigned to one of 6 treatment groups to receive IV midazolam (0.03 mg/kg) or placebo, followed 5 minutes later by one of three IV preinduction doses of lidocaine: 0.5, 1.0, or 1.5 mg/kg.

MEASUREMENTS

BIS values were recorded before administration of lidocaine and at 30-second intervals afterwards for three minutes. The primary endpoint was the average BIS level recorded.

MAIN RESULTS

Baseline BIS values were lower in the midazolam group (94 ± 4 vs. 90 ± 7, P < 0.001). There was no significant decrease in BIS values in the placebo group for any of the three lidocaine doses. However, in the midazolam groups, significant decreases in BIS levels versus baseline values were measured.

CONCLUSION

IV lidocaine decreases BIS in the presence of midazolam, suggesting that the effect of lidocaine on BIS is not direct, but rather results from modulation by midazolam.